1500 rpm Stumble

Bikes been running pretty good lately but i have noticed a little stumble just when i take off from a stop, it idles perfect but if i try to hold the throttle at 1500rpm it will slowley sputter and die but anything above or below 1500 it runs perfect and revs up fine with no hesitation, the carbs have been totally cleaned with new shaft seals and all, and are in sync. Could this be a pilot screw problem?
If i throw the chokes on when it starts to stumble at 1500 it clears right up.
Thanks Doug

 

Valves in spec?

How did you set the float levels?

Sync method?

 

Valves are in spec.
Set the floats using the clear line method.
sync. With gauges.

 

Wel i re synced the carbs and had one way out for some reason now it run like a champ again. I did a plug chop and here is what they look like. i think it looks a little lean.
I'm running a 4 into 1 header with a stock airbox & filter I am 3 bigger on the main jets and 1 bigger on the pilots & the pilot screws are out 3 1/4 turns I would sure think this would be enough not to be lean.

 

Those look fine if you pay attention to the ground strap and flame ring; as far as coloration on the insulators, the only way to really tell is to compare them to a brand new, un-run plug. The 550s tend to keep their plugs cleaner than the big bikes do their larger plugs.

Ride it, check the plugs occasionally.

 

Thanks Fitz that's what I'm gonna do ride it!